1. Field of the Invention
The present invention relates to a photo-electric converter, and more particularly to a photo-electric converter used for reading an image in facsimile machine, image reader, digital copying machine or electronic backboard
2. Related Background Art
In order to reduce the size and enhance the performance of a facsimile machine or image reader, a web type line sensor having a unity magnification optical system as a photo-electric converter has been developed. In the past, such a line sensor has comprised a linear array of photo-electric conversion elements having a signal processing IC (integrated circuit) consisting of switching elements connected thereto. However, the number of such photo-electric conversion elements amounts to 1728 for a size A4 in the facsimile G3 specification and hence a number of signal processing IC's are required. As a result, the number of packaging steps increases and the manufacturing cost and reliability are not satisfactory. On the other hand, in order to reduce the number of signal processing IC's and the number of packaging steps, a matrix wiring has been adapted.
FIG. 1 shows a block diagram of a matrix-wired photo-electric converter. Numeral 1 denotes a photoelectric conversion element unit, numeral 2 denotes a scan unit, numeral 3 denotes a signal processing unit and numeral 4 denotes a matrix wiring unit. FIG. 2 shows a plan view of a prior art matrix wiring unit and FIGS. 3(a) and 3(b) show A-A' and B-B' cross-sectional views of FIG. 2.
In FIGS. 3(a) and 3(b), numeral 601 denotes a substrate, numerals 602 to 605 denote discrete electrodes, numerals 607 to 609 denote common lines and numeral 610 denotes a through-hole which ohmically contacts the discrete electrodes to the common lines. Numeral 606 denotes an insulating layer.
In such a matrix-wired photo-electric converter, the number of signal processing circuits in the signal processing unit 3 may be equal to the number of output lines of the matrix. Thus, the signal processing unit may be compact and cost reduction of the photoelectric converter is attained.
However, the prior art matrix-wired photoelectric converter has the following problems.
Since weak outputs of the photo-electric conversion elements are read through the matrix wiring, crosstalk occurs between the output signals, unless stray capacitance at insulated crosspoints of the discrete output electrodes of the photo-electric conversion elements and the common line of the matrix is sufficiently small. This is a severe restriction of the selection of interlayer insulation material and the design of the dimension of the matrix.
Since the matrix common lines are arranged longitudinally, they may be as long as 210 mm for a line sensor of a size A4. Accordingly, unless a line-to-line capacitance between the common lines is sufficiently small, the crosstalk occurs between the output signals. This leads to increase of size of the matrix unit.
A pitch of the discrete output electrodes of the photo-electric conversion elements may be 125 .mu.m in the photo-electric converter having a resolution of 8 lines/mm. Accordingly, unless the line-to-line capacitance of the discrete electrodes is sufficiently small, crosstalk occurs between the output signals.